This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Shifts in the direction of gaze require a combination of eye and head movements. One popular model posits that the brain controls the accuracy of the overall gaze movement, i.e., the sum of the eye and head movement, rather than just the eye component alone. In normal animals, this proposal is impossible to test because the timing of the gaze shift and its eye movement component are tightly linked. However, after the semicircular canals, which sense head rotation, are disabled by plugging, the eye stops well before gaze lands on target. In this condition, therefore, we can assess whether the discharge of the neuronal elements in the brainstem that are active during gaze shifts is better timed with the gaze or eye movement. The brainstem generator that drives gaze shifts consists of two populations of neurons. One discharges a burst of spikes that begins before and continues during the gaze shift and its eye movement component. The other neurons exhibit a pause in their high resting rates during the same interval. After the canals have been plugged, the burst and pause both are better timed with the end of the eye movement than with the end of the gaze movement. Therefore, the discharge patterns of both types of neurons ends much too early to help terminate the gaze shift. In contrast, they have the timing appropriate to control the duration and hence accuracy of the eye movement component of the gaze shift. These data are inconsistent with a model of the brainstem generator that controls the overall gaze shift.